Simpson, who is eight months pregnant with her first child, has been called "huge," "a house," and "an absolute porker," the latter coming from a Florida OB/GYN. "The Hunger Shames," Jezebel called it.

"I hate how judgmental people are about pregnant women," said Dr. Marjorie Greenfield, chief of obstetrics and gynecology at University Hospitals Case Medical Center in Cleveland. "You have to have a thick skin and recognize that people don't have the right to criticize you. No one's closer to this pregnancy than you are."

Doctors say putting on 25 to 35 pounds during pregnancy is healthiest. And while it's unclear how much weight Simpson has gained, critics have accused her of "letting go" and being a bad role model for pregnant women.

"No one should ever look like Jessica Simpson," Dr. Tara Solomon, a OB/GYN in Fort Lauderdale, Fla. told Slate. "She's an absolute porker… I cannot believe how heavy she is."

Simpson has taken flack over her figure before. The "Fashion Star" mentor's weight has been tabloid fodder for years. But pregnancy weight is a touchy topic. Gaining too much or too little can harm both mom and baby.

"Early pregnancy weight gain is associated with an increased risk of developing diabetes during pregnancy," said Greenfield. "Weight gain also tends to make bigger babies, which means a tighter fit through the birth canal."

Gaining too little weight, on the other hand, can affect the baby's growth, "and that's really not a healthy situation," said Greenfield. "Surprisingly, gaining too little weight actually increases the chance of the child being obese later in life."

Gaining a healthy amount of weight during pregnancy doesn't have to be hard, Greenfield said. Eating a balanced diet with plenty of fruits, vegetables, whole grains and lean sources of protein is a smart way to stay within the recommended range.

"If we all had fantastic, healthy diets to begin with, we wouldn't need to do anything differently during pregnancy. The only difference is you need 300 extra calories a day," she said, "That's an apple and a yogurt. You're certainly not eating for two adults."

Greenfield said moms-to-be should practice moderation and listen to their appetites.

"It's a good chance to build habits for the rest of your life," she said.

Simpson said she has "a lot of amniotic fluid," which may be accounting for some of the weight.

"A significant portion of weight gain for some people is water retention, and you don't have control over that," said Greenfield. "People can look very puffy, and they're just going to pee it out two weeks after the delivery."

One of the biggest problems with gaining too much weight during pregnancy is the inability to lose it later.

"After six months, you may never get it off," said Greenfield. "We say nine months to gain and six months to lose. Excess pregnancy weight gain is a big contributor to obesity."

Eating a healthy diet and exercising can help women shed the post-pregnancy pounds. But Greenfield said it's no easy feat.

"It's hard because there are so many things you're supposed to be doing: breastfeeding, maintaining your marriage, including your parents, writing thank-you notes for baby shower gifts, getting sleep," she said. "You can't do them all. We all have to just muddle through and do our best."